EP0463853B1

EP0463853B1 - Vacuum chuck

Info

Publication number: EP0463853B1
Application number: EP91305730A
Authority: EP
Inventors: Tetsuzo C/O Canon Kabushiki Kaisha Mori; Mitsuji C/O Canon Kabushiki Kaisha Marumo; Kazunori C/O Canon Kabushiki Kaisha Iwamoto; Yuji C/O Canon Kabushiki Kaisha Chiba; Kazuyuki c/o Canon Kabushiki Kaisha Kasumi
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1990-06-29
Filing date: 1991-06-25
Publication date: 1998-11-04
Anticipated expiration: 2011-06-25
Also published as: DE69130434T2; EP0463853A1; US5191218A; DE69130434D1

Description

FIELD OF THE INVENTION AND RELATED ART

This invention relates generally to a vacuum attraction type substrate holding device for holding a substrate through vacuum attraction applied to the bottom face of the substrate. More particularly, the invention is concerned with such a vacuum attraction type substrate holding device which is usable in a semiconductor device manufacturing apparatus, for example, as a vacuum chuck. In another aspect, the invention is concerned with an exposure method and apparatus which uses such a vacuum attraction type holding device, for manufacture of semiconductor devices.

In the manufacture of semiconductor devices, a substrate holding device for holding a substrate such as a semiconductor wafer, onto which a pattern for preparation of semiconductor devices is to be lithographically transferred, is used. An example is a vacuum attraction type wafer holding device (vacuum chuck) wherein a wafer is held through vacuum attraction applied to the bottom face thereof (Patent applications JP-A-1 14703 or EP-A-357 424).

As regards an exposure apparatus usable with such a substrate holding device, there are many types of exposure apparatuses. Examples are: exposure apparatuses using deep UV light as an exposure light source, and X-ray exposure apparatuses which uses X-rays contained in synchrotron orbital radiation (Patent Application No. JP-A-2 100 311).

The document EP-A-408 350, published on 16.01.91 and comprised in the state of the art in accordance with Article 54(3) EPC, discloses a vacuum attraction device for holding a wafer in an exposure apparatus. In said device a pressure gauge for measuring the pressure between the wafer and the table has its own passageway, separated from the vacuum passageway.

For lithographic transfer of a ultra-fine pattern onto a wafer, use of a high-precision wafer holding device is necessary. Further, in some exposure apparatuses such X-ray exposure apparatuses wherein a mask and a wafer are placed opposed to each other with a very small gap (proximity gap) maintained therebetween, a heat is produced by the application of exposure energy used for the lithographic transfer of a mask pattern. Thus, it is desirable that a used wafer holding device has a structure effective to remove the heat from the wafer efficiently, since, if not so, a possible temperature rise in the wafer or possible thermal deformation of the wafer damages the pattern transfer precision.

It is accordingly an object of the present invention to provide a substrate holding device of vacuum attraction type by which a substrate can be held with very high precision.

According to the invention there is provided a vacuum-attraction holding device, comprising:

a holding base having an attracting surface for holding a substrate thereon;

a first passageway formed in said holding base for supplying vacuum to said holding base to cause the substrate to be attracted to said attracting surface; and

a pressure sensor;

characterised in that a second passageway is formed within said holding base, separate from said first passageway, wherein the second passageway is open to said attracting surface so that said second passageway serves to communicate said pressure sensor with said attracting surface, and in that said pressure sensor is provided within said holding base.

In accordance with an aspect of the present invention, the pressure for holding a substrate can be controlled with very high precision. Thus, when such a holding device is incorporated into a semiconductor device manufacturing exposure apparatus, precise transfer of an ultra-fine pattern onto a substrate, such as a wafer, is assured and, therefore, enhanced yield and productivity are ensured.

It is another aspect of the present invention to provide a substrate holding device of vacuum attraction type by which the pressure in a clearance between the substrate and the holding base may be controlled precisely to maintain therebetween a small contact heat resistance not greater than a predetermined level.

In a vacuum-attraction substrate holding device of the present invention, a pressure sensor is provided in a holding base to detect the pressure in a closed space or in a suction passageway. This makes it possible to detect the pressure at the bottom of the substrate very precisely, without being affected by the ambience in which the holding device is placed or by the condition of the bottom face of the substrate.

The pressure sensor may detect a differential pressure between the inside pressure of the closed space or of the suction passageway and the outside pressure (atmospheric pressure) introduced through an introduction passageway formed in the holding base. In that occasion, as compared with direct detection of the inside pressure of the closed space or of the suction passageway, it is possible to detect the pressure difference between the top and bottom faces of the substrate even if the outside pressure of the holding device changes.

The substrate holding device is provided with a gauging passageway for communicating a vacuum gauge and a chucking surface of a holding base. Almost all the gas in the gauging passageway can be discharged outwardly with the execution of evacuation to some degree. Thus, the level of pressure as measured by the pressure gauge is equal to the pressure in a small clearance defined between the chucking surface of the holding base and the bottom face of the substrate. By controlling appropriate means on the basis of an output signal from the vacuum gauge so that the pressure in the small clearance is held at a predetermined level, it is possible to retain the desired level of pressure in the small clearance precisely.

Valve means controlled through a control means may be interposed between the gauging passageway and an evacuation passageway. The valve means may be so controlled that, after it is opened by the control means, the vacuum attraction starts. This assures quick discharging of the gas in the gauging passageway through the valve means, such that a desired level of pressure can be attained in the small clearance precisely and quickly.

An exposure method and apparatus according to a still further aspect of the present invention may use the substrate holding devices described above, and because of the attainment of high precision for the measurement and/or control of the pressure in the small clearance, high pattern transfer precision can be assured.

These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A and 1B are a top plan view and a sectional view, respectively, of a wafer holding-device without the present invention.

Figures 2A and 2B are a top plan view and a sectional view, respectively, of a wafer holding device included for reference purposes only.

Figure 3 is a graph showing the relationship between the evacuation time and the differential pressure.

Figure 4 is a flow chart of the control operation in the device of Figures 2A and 2B.

Figures 5A and 5B are a top plan view and a sectional view, respectively, of a wafer holding device according to the present invention.

Figures 6 to 8 are fragmentary perspective views, respectively, showing modified forms of wafer chucking surfaces.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before describing details of the present invention, a problem underlying the present invention will first be explained.

Figures 1A and 1B show an example of vacuum attraction type wafer holding device without the present invention.

This wafer holding device includes a holding base 401 for holding a wafer (not shown) through vacuum attraction applied to the bottom face of the wafer; an evacuation pump 406 for applying vacuum attraction to the wafer; a piping member 404 for communicating the evacuation pump 406 with a suction passageway 408 (to be described later); and a valve 407 provided at a portion of the piping member 404 between the evacuation pump 406 and the holding base 401. It further includes a pressure sensor 405 provided at a portion of the piping member 404 between the valve 407 and the holding base 401, for detecting a differential pressure between the inside pressure of the piping member 404 and an ambience pressure (external pressure) as introduced from an introduction passageway 411. It further includes a control circuit 410 which is responsive to an output signal of the pressure sensor 405 to produce an instruction signal, for starting a subsequent step (e.g. a signal designating start of movement of the wafer holding device to a wafer exposure station) when the differential pressure represented by the pressure sensor output signal increases beyond a predetermined level.

The holding base has an attracting surface 402, two concentric ring-like grooves 409₁ and 409₂ formed in the attracting surface, suction ports 403 and a suction passage 408 for communicating the suction ports 403 with the piping member 404. The attracting surface has been finished to attain desired flatness of a wafer as it is attracted to this surface through vacuum attraction. One of the suction ports 403 is formed at a center of the attracting surface 402, four of them are formed in one of the grooves 409₁ and 409₂, and the remaining four suction ports are formed in the other groove. The valve 407 when closed is effective to communicate the inside of the piping member 404 with the external space and, when opened, is effective to communicate the inside of the piping member with the evacuation pump 406.

In this wafer holding device, a wafer to be held by vacuum attraction is conveyed by means of a known type conveying hand (not shown) to a position whereat it contacts to the attracting surface 402 of the holding base 401. After this, the valve 407 is opened and the gas contained in a space (closed space) defined by the conveyed wafer, the attracting surface 402 and the two concentric grooves 409₁ and 409₂ formed in the attracting surface 402, is discharged by means of the evacuation pump 406 through the suction ports 403, the suction passageway 408 and the piping member 404. By this, the bottom face of the wafer is vacuum-attracted. Here, the pressure sensor 405 detects the differential pressure between the inside pressure of the piping member 404 and the external pressure, and produces and applies a signal, representing this differential pressure, to the control circuit 410. As it is discriminated by this control circuit 410 that the differential pressure represented by the pressure sensor 405 signal becomes greater than a predetermined level, the control circuit 410 produces an instruction signal such as described hereinbefore.

For releasing the vacuum attraction of the wafer, on the other hand, the valve 407 is closed and an external gas is supplied into the piping member 404.

In this wafer holding device, the pressure sensor 405 is disposed at a portion of the piping member 404 which is between the valve and the holding base 401 and thus, to be exact, the pressure sensor 405 senses the pressure in that portion of the piping member 404. Since the structure of the piping member 404 and the suction passageway 408 is complicated, there is a possibility that the sensed pressure is different from the pressure at the wafer attracting surface.

Figures 2A and 2B show a substrate holding device of vacuum attraction type according to an embodiment included for reference purposes only. In this embodiment, a wafer holding device serves for holding a semiconductor wafer through vacuum attraction onto which wafer a pattern for preparation of semiconductor devices is to be lithographically transferred. This wafer holding device may be incorporated into a deep UV or X-ray exposure apparatus.

The wafer holding device of this embodiment includes a holding base 1 for holding a wafer (not shown) through vacuum attraction applied to the bottom face of the wafer; an evacuation pump 6 for applying vacuum attraction to the wafer; a piping member 4 for communicating the evacuation pump 6 with a suction passageway 8 (to be described later); and a valve 7 provided at a portion of the piping member 4 between the evacuation pump 6 and the holding base 1. The holding base has an attracting surface 2, two concentric ring-line grooves 9₁ and 9₂ formed in the attracting surface, suction ports 3 and a suction passage 8 for communicating the suction ports 3 with the piping member 4. The attracting surface has been finished to attain desired flatness of a wafer as it is attracted to this surface through vacuum attraction. One of the suction ports 3 is formed at a center of the attracting surface 2, four of them are formed in one of the grooves 9₁ and 9₂, and the remaining four suction ports are formed in the other groove. The structure described above is the same as that shown in Figures 1A and 1B.

Differences from the Figures 2B and 1B reside in that: Pressure sensor 5 is provided inside the holding base 1 and it detects a differential pressure between the inside pressure of the suction passageway 8 and an ambience pressure (external pressure) introduced through an introduction passageway 11 which communicates the pressure sensor 5 with the external space. Timer 12 is provided to measure the evacuation time. Control circuit 10 includes discriminating means 10₁ for discriminating whether the evacuation time, as indicated by the timer 12 when the inside pressure of the suction passageway 8 represented by an output signal of the pressure sensor 5 becomes lower than a predetermined level, is longer or not longer than a predetermined time period.

As in the example of Figures 1A and 1B, the valve 7 when closed is effective to communicate the inside of the piping member 4 with the external space and, when opened, is effective to communicate the inside of the piping member with the evacuation pump 6.

Referring to Figures 3 and 4, the operation of the wafer holding device of this embodiment will be explained.

A wafer to be held by vacuum attraction is conveyed by means of a known type conveying hand (not shown) to a position whereat it contacts to the attracting surface 2 of the holding base 1. After this, the valve 7 is opened and the gas contained in a space (closed space) defined by the conveyed wafer, the attracting surface 2 and the two concentric grooves 9₁ and 9₂ formed in the attracting surface 2, is discharged by means of the evacuation pump 6 through the suction ports 3, the suction passageway 8 and the piping member 4. By this, the bottom face of the wafer is vacuum-attracted. Here, the pressure sensor 5 detects the differential pressure P between the inside pressure of the suction passageway 8 and the external pressure, and produces and applies a signal, representing this differential pressure P, to the control circuit 10.

Here, the relationship between the evacuation time t from start of vacuum attraction and the differential pressure P represented by the output signal of the pressure sensor 5, in an occasion where there is no leakage of external gas into the closed space, is such as depicted by a solid line in Figure 3.

More specifically, before start of vacuum attraction of the wafer (evacuation time t = 0), since the valve 7 is once closed and the inside of the piping member 4 is communicated with the external space, the inside pressure of the suction passageway 8 becomes equal to the external pressure. Thus, the differential pressure P = 0 (Torr). After this, as the vacuum attraction of the wafer starts, the inside pressure of the suction passageway decreases with the progress of evacuation. As a result, the differential pressure P increases and, at an evacuation time t = t₁ (point A), the differential pressure P = P_X1; at an evacuation time t = t₂ (point C), the differential pressure P = P_X2; and at an evacuation time t = t₃ (point E), the differential pressure P = P_X3.

Here, if the difference between the pressures at the top face and the bottom face of the wafer, necessary for attaining the wafer holding through vacuum attraction (such difference will be referred to as "specific differential pressure"), is equal to the differential pressure P_X1 at point A in Figure 3, since the differential pressure between the inside pressure of the suction passageway 8 and the external pressure as detected by the pressure sensor 5 corresponds to the difference between the pressures at the top face and the bottom face of the vacuum-attracted wafer with good precision, the control circuit 10 may produce an instruction signal for starting a succeeding step (e.g. a signal designating start of movement of the holding device to a wafer exposure station) when it is discriminated that the differential pressure P represented by the output signal of the pressure sensor 5 has become higher than said specific differential pressure P₀ (= P_X1), namely, that the inside pressure of the suction passageway 8 has become lower than the predetermined level. By this, it is possible to accomplish the vacuum attraction of the wafer with a smallest necessary attracting force and in a shortest necessary evacuation time.

The foregoing description has been made on an assumption that there is no external gas leakage into the closed space. Actually, however, due to distortion of the wafer or adhesion of foreign particles to the wafer, or from the positional relationship between the wafer and the attracting surface 2 as the wafer is placed on the latter, external gas leaks into the closed space occurs. The relationship between the evacuation time t from start of vacuum attraction and the differential pressure P represented by the output signal of the pressure sensor 5 in this occasion, is such as depicted by a broken line in Figure 3. It is seen that, at the same evacuation time t, the differential pressure P is smaller than that in a case where no external gas leaks into the closed space. Namely, at the evacuation time t = t₁ (point B), the differential pressure P = P_Y1 (P_Y1 < P_X1) and, at the evacuation time t = t₂ (point D), the differential pressure P = P_Y2 (P_Y2 < P_X2).

However, in the wafer holding device of the present embodiment, since the differential pressure P represented by the output signal of the pressure sensor 5 has a good correspondence with the difference between the pressures at the top face and the bottom face of the vacuum-attracted wafer, the control circuit 10 may produce an instruction signal such as described above when it is discriminated that the differential pressure P has become higher than said specific differential pressure P₀ (= P_X1) (namely, at the evacuation time t = t₂ in Figure 3). By this, irrespective of external gas leakage into the closed space, it is possible to accomplish the vacuum attraction of the wafer with a smallest necessary attracting force and in a shortest necessary evacuation time.

Further, the relationship between the evacuation time t and the differential pressure P as there occurs maximum allowable leakage of external gas into the closed space, may be detected beforehand and, in this occasion, such evacuation time t at which the differential pressure P becomes equal to said specific differential pressure P₀ (= P_X1), namely, the evacuation time t = t₃ (point F) in the case of the broken line in Figure 3, may be detected beforehand. If in this occasion the differential pressure P represented by the output of the pressure sensor 5 does not become greater than said specific differential pressure P₀ (= P_X1) even after the evacuation time t from start of the vacuum attraction of the wafer as measured through the timer 12 becomes longer than a predetermined evacuation time T₀ (= t₂), the control circuit 10 may produce an instruction signal designating interruption of the wafer vacuum attraction or a signal indicating an abnormal state.

Thus, when the control circuit 10 and the discriminating means 10₁ operate in accordance with the flow chart of Figure 4, the yield as well as the throughput of the exposure apparatus can be enhanced.

More specifically, as the wafer vacuum attraction starts, the control circuit 10 reads an output signal of the pressure sensor 5 and an output signal of the timer 12 (step 71). The discrimination means 10₁ discriminates whether the evacuation time t represented by the output of the timer 12 is longer or not longer than the predetermined evacuation time T₀ (step 72). If the former is longer than the latter, the control circuit 10 produces a signal which, as an example, indicates an abnormal state (step 73). If, on the other hand, the former is not longer than the latter, discrimination is made as to whether the differential pressure P represented by the output signal of the pressure sensor 5 is greater or not greater than said specific differential pressure P₀ (step 74). If the former is not greater than the latter, the sequence goes back to step 71. If the former is greater than the latter, the control circuit 10 produces an instruction signal such as described hereinbefore (step 75).

For releasing the vacuum attraction of the wafer, the valve 7 is closed and external gas is introduced into the piping member 4.

In the wafer holding device of the present embodiment, the pressure sensor may be provided in a bottom portion of the holding base 1, and a gas in the suction passageway 8 may be introduced from a position adjacent to the bottom of the holding base 1. Thus, if it is desired to provide cooling water pipe means in the holding base 1 for cooling a wafer during exposure thereof, it is possible to secure the inside space for the pressure sensor 5.

Figures 5A and 5B show a wafer holding device according to the present invention which is usable in an X-ray exposure apparatus, for example.

The wafer holding device of this embodiment differs from the embodiment shown in Figures 2A and 2B in that: As shown in Figure 5B, pressure sensor 35 provided in a holding base 31 serves to detect a differential pressure between (i) an inside pressure of a closed space introduced from an introduction port 46 (formed in outer one (39₂) of two concentric ring-like grooves defined in an attracting surface 32 of the holding base, and at a position as illustrated in Figure 5B) and through a second introduction passageway 45 separate from the passageway 38 to which suction is applied and (ii) an ambience pressure (external pressure) introduced through a first introduction passageway 41.

In the holding device of the invention, since the pressure sensor 35 detects the differential pressure by using the pressure in the closed space, it is possible to detect the pressure at the bottom face of the vacuum-attracted wafer with higher precision as compared with the Figure 2 embodiment.

The control circuit 40 serves only to produce an instruction signal designating start of a subsequent step, if it is discriminated that the pressure in the closed space represented by the output signal of the pressure sensor 35 has become lower than a predetermined pressure.

Thus, if it is desired to provide cooling water pipe means in the holding base 31 for cooling a wafer during exposure thereof, it is possible to secure the inside space for the pressure sensor 35.

The device of the invention may be equipped with a timer for measuring the evacuation time, and the control circuit 40 may be provided with discriminating means such as at 10₁ in Figure 2B. In that occasion, the control circuit 40 may produce an instruction signal for starting a subsequent step (e.g. a signal designating start of movement of the holding device to a wafer exposure station in the X-ray exposure apparatus), after it is discriminated that within a predetermined evacuation time the differential pressure represented by the output of the pressure sensor 35 has become greater than a specific differential pressure, namely, that the inside pressure of the closed space has become lower than a predetermined pressure.

In the foregoing description, the pressure sensor 5 shown in Figure 2B and the pressure sensor 35 shown in Figure 5 each detects a differential pressure between the inside pressure of the suction passageway 8 (or of the closed space) and the external pressure. However, it may be one adapted to directly detect the inside pressure of the suction passageway 8 (or of the closed space). Particularly where the external pressure is controlled at a constant level, there is no specific necessity of detecting the differential pressure. Since, in that occasion, it is not necessary to introduce the external gas to the pressure sensor 5 or 35, the provision of the introduction passageway 11 or the first introduction passageway 41 is not necessary.

Where the inside pressure of the suction passageway 8 or of the closed space is to be directly detected, a pressure sensor comprising a load cell may be disposed at a desired position in the suction passageway or in the closed space.

The configuration of the attracting surface of the holding base is not limited to the disclosed form, and a pin-chuck type wherein a plurality of columnar projections are provided on a surface of the holding base, to be opposed to the bottom face of a wafer, may be used.

Next, various forms of the chucking surface of the wafer chuck will be explained.

As shown in Figure 6, the wafer chuck 206 has two concentric ring-like grooves 206₂ formed in the chucking surface 206₁ as well as another groove (recess) 206₂ formed at a central portion of the chucking surface 206₁. The evacuation passageway 211 are branched to be opened to the ring-like grooves 206₂ and the central recess 206₂. In this embodiment, the gauging passageway 230 opens to a portion of the chucking surface 206₁ which is between the central recess 206₂ and the inner one of the two ring-like grooves 206₂.

Figure 7 shows another form of chucking surface of a wafer chuck.

In the wafer chuck 226 of this embodiment, one concentric ring-like groove 226₂ is formed at an outer peripheral portion of the chucking surface 226₁. Branched ends of an evacuation passageway 211 are opened to upper and lower portions and right-hand and left-hand portions (as viewed in the drawing) of the groove 226₂ (upper and lower branched ends of the evacuation passageway 211 are not shown). Gauging passageway 230 is opened to a central portion of the chucking surface 226₁. This portion of the structure described above is different from the wafer chuck 206 of Figure 6.

The wafer chuck 226 of this example is effective to attain a larger contact area between a wafer 205 and the chucking surface 226₁ and, for this reason, it is possible to reduce the heat contact resistance as compared with the wafer chuck 206 of the Figure 6 embodiment.

Figure 8 shows another form of chucking surface of a wafer chuck.

Like the wafer chuck 226 shown in Figure 7 in the wafer chuck 236 of this embodiment, one concentric ring-like groove 236₂ is formed at an outer peripheral portion of the chucking surface 236₁. Branched ends of an evacuation passageway 211 are opened to upper and lower portions and right-hand and left-hand portions (as viewed in the drawing) of the groove 236₂ (upper and lower branched ends of the evacuation passageway 211 are not shown). Gauging passageway 230 is opened to a central portion of the chucking surface. Additionally, three narrow grooves 236₃ are formed equiangularly so as to communicate the open end of the gauging passageway 230 with the concentric groove 236₂.

This wafer chuck 236 has an advantage that the three narrow grooves 236₃ can serve as evacuation passageways and, for this reason, an enhanced efficiency of evacuation of He gas in the gauging passageway 230 is attainable.

In the embodiments of wafer chuck (206, 226, 236) shown in Figures 6 - 8, the evacuation passageway 211 is opened to the groove at four sites. However, provided that the openings have good symmetry, the number is not limited to "four".

While in the foregoing the invention has been described with reference to examples of X-ray exposure apparatus, the invention is applicable to any type of exposure apparatus such as one using light, for example, wherein it has a substrate holding device by which a substrate is held through a pressure difference between the top and bottom faces thereof while the substrate is maintained at a constant temperature.

Further, the article to be held by a substrate holding device of the present invention is not limited to a wafer. It may be a substrate for a liquid crystal display on which thin film transistors and the like are to be formed.

Claims

A vacuum-attraction holding device, comprising:

a holding base (31) having an attracting surface (32) for holding a substrate thereon;

a first passageway (38) formed in said holding base for supplying vacuum to said holding base to cause the substrate to be attracted to said attracting surface; and

a pressure sensor (35);

characterised in that a second passageway (45) is formed within said holding base (31), separate from said first passageway, wherein the second passageway (45) is open to said attracting surface so that said second passageway serves to communicate said pressure sensor (35) with said attracting surface (32), and in that said pressure sensor (35) is provided within said holding base (31).
A device according to claim 1, further characterized in that it comprises a third passageway (41) formed within said holding base (31) and open to the ambience pressure surrounding said holding base, wherein said third passageway serves to communicate said pressure sensor with said ambience pressure, said pressure sensor sensing a difference between the pressure in said second passageway and the pressure of said ambience surrounding the holding base.
An exposure apparatus including a vacuum attraction holding device as claimed in claim 1 or 2, comprising

exposing means for exposing a substrate held on said holding base with radiation; and

control means (40) serving to generate a process instruction signal if it is determined that the pressure in the second passageway open to said attracting surface is less than a predetermined pressure.
An exposure apparatus as claimed in claim 3, further characterised in that there are provided means for moving the holding device to a wafer exposure position on generation of said process instruction signal.
An apparatus according to claim 3 or 4, wherein said control means controls said at least one of the holding device and the exposing means when a pressure of a predetermined level is attained between the substrate and said attracting surface.
An apparatus according to claim 3 or 4, further comprising a communication passageway (34) for communicating said first passageway (38) with an evacuation pump (36) and a valve (37) for opening and closing said communication passageway.
A semiconductor wafer processing method, for manufacture of semiconductor devices, said method comprising the steps of:

providing a wafer holding base (31) formed with a pressure sensor within said base, a wafer attracting surface (32), a first passageway (38) within the body of the base and a second passageway (45) formed within the body of the base separate from said first passageway and open to said attracting surface so that said second passageway serves to communicate said pressure sensor with said attracting surface;

placing a semiconductor wafer (205) on the holding base;

supplying vacuum to the holding base through the first passageway (38) to cause the wafer to be attracted to the attracting surface by vacuum attraction;

detecting through the second passageway, the pressure related to the vacuum attraction; and

exposing the wafer held by the holding base, with radiation;

wherein at least one of the wafer holding operation through the holding base and the wafer exposing operation is controlled on the basis of the pressure detected through the second passageway.
A method according to claim 7, further comprising providing a mask having a circuit pattern, wherein the circuit pattern of the mask is transferred to the wafer by the wafer exposing operation.